The present invention relates to a control system for an automatic vehicle transmission.
Recently, it is required that automatic vehicle transmissions have some measure to alleviate select shock caused by engagement of a certain friction element or elements upon selecting a forward drive or a reverse drive from the neutral condition of the transmission. Conventionally, in order to control the rise of a servo actuating fluid pressure supplied to a friction element to be engaged, an accumulator has been used. The accumulator has an expandable chamber communicating with the servo chamber of the friction element. The expandable chamber is defined by a piston biased by a spring. The spring yields to allow movement of the piston in such a direction as to expand the volume of the expandable chamber after the chamber has begun to be supplied with fluid pressure, thus allowing gradual fluid pressure build-up within the friction element. Thus, the friction element is gradually engaged to alleviate select shock. As is known, the rate of increase in fluid pressure is mainly dependent on a load-flexure characteristic of the piston spring, and the rate of increase of the fluid pressure must be set as small as possible for increased effectiveness of select shock alleviation. However, if the rate of increase of the fluid pressure is decreased, the completion timing of the select operation is delayed, resulting in poor operability of the vehicle.